Light-guiding system comprising a number of light transmission rods

ABSTRACT

A light-guiding system comprising a plate-like light-guiding member ( 1 ) provided with a lateral surface for coupling in light into said light-guiding member ( 1 ). The ends of a number of light transmission rods ( 6 ) are connected to said lateral surface, while said light-guiding member ( 1 ) and said light transmission rods ( 6 ) are one piece of the same material.

A light-guiding system comprising a number of light transmission rodsThe invention relates to a light-guiding system comprising a plate-likelight-guiding member provided with a lateral surface for coupling inlight into said light-guiding member.

Such a system is disclosed in US-A-2002/0167820. This publicationdescribes a light-guiding system for improving the lighting conditionsof the passenger compartment of a motor vehicle, whereby a plate-likelight-guiding member is arranged in the area of the interior lining ofthe vehicle roof. Light is coupled in into the light-guiding memberthrough one or more lateral surfaces of the light-guiding member, andlight is emitted in a homogeneous manner into the passenger compartmentof the vehicle through the large front surface of the light-guidingmember.

Depending on the refractive index of the material of the light-guidingmember, the light will be reflected back into the light-guiding memberby the surfaces of said member when the surfaces are smooth and when theangle of incidence is greater than a certain value, i.e. the angle oftotal reflection. The angle of incidence is the angle between the lightbeam and a line perpendicular to the surface to which the light beam isdirected.

Appropriate materials for guiding light are transparent thermoplastics,in particular polymethyl methacrylate (PMMA) or polycarbonate (PC). Suchmaterials can be shaped, for example, by an injection molding process,by an extrusion process, or by a material-removing laser operation.

Light may be coupled in into the light-guiding member by means of alight-generating unit, such as a fluorescent tube, extending along thelateral surface of the light-guiding member. As an alternative, a numberof light-emitting elements, such as light-emitting diodes (LEDs) may bearranged in a row along said lateral surface. However, in all thesecases, only a portion of the light radiated by the light-generating unitwill directly reach the lateral surface for coupling in the light intothe light-guiding member. The use of a reflector behind thelight-generating unit can increase the portion of the light radiationthat reaches said lateral surface, but still there is much more lightgenerated near said lateral surface than can be coupled in into thelight-guiding member.

Furthermore, it is often desired that the directions of the light beamscoupled in into the light-guiding member enclose relatively small angleswith the direction perpendicular to said lateral surface. That willimprove the guidance of the light in the light-guiding member. Speciallenses may be used to achieve such a direction of the light beams.

The object of the invention is to provide a light-guiding system whereinlight is coupled in through the lateral surface of a plate-likelight-guiding member, wherein there is no loss of light near saidlateral surface, and wherein the light beams of the light radiation canbe easily directed at small angles to the direction perpendicular tosaid lateral surface.

In order to accomplish that objective, the ends of a number of lighttransmission rods are connected to said surface, said light-guidingmember and said light transmission rods being one integral piece of thesame material. The light transmission rods will guide light into saidlight-guiding member without any loss of light, because the light beamsstay in the same light-guiding material and the light in the lighttransmission rods can easily be given directions at small angles to thelongitudinal direction of the light transmission rod, so that thedirection of the coupled-in light beams is substantially perpendicularto said lateral surface.

In one preferred embodiment, there are at least four, preferably morethan eight, or many more light transmission rods positioned near saidlateral surface, parallel to each other in a plane perpendicular to saidlateral surface, such that the distance between the light transmissionrods, near said surface, is preferably less than 5 mm, more preferablybetween 1 mm and 2 mm. Preferably, each light transmission rod has adiameter between 0.2 mm and 5 mm, more preferably between 1 mm and 3 mm.The light transmission rods may also be positioned in more parallelplanes perpendicular to said lateral surface.

To achieve a convenient connection between the light transmission rodsand the light-guiding member in which there is no transitional surface,the light transmission rods and the light-guiding member are of one andthe same homogeneous piece of material. Preferably, said light-guidingmember and the light transmission rods are produced by an injectionmolding operation, both being manufactured jointly in one operation.

In one preferred embodiment, at least a portion of a light transmissionrod has a hexagonal or a square transverse section. Such a shape of thelight transmission rods makes it possible to combine a number of lighttransmission rods into a bundle without deforming the rods and withoutspace between the rods. The light transmission rods can be easily boundtogether without heating as a result of this.

The transverse section of the light transmission rods may also varyalong its length, i.e. in one preferred embodiment at least a portion ofa light transmission rod has an increasing diameter in a directiontowards the light-guiding member. The light beams will thus become moreand more parallel when passing through the light transmission rod. Suchan increase of the diameter is preferably applied near the light-guidingmember to which the rods are connected, the diameter of the lighttransmission rods near said member being preferably more than 1.5 times,more preferably more than twice, the diameter further away from saidlight-guiding member. Such an increasing diameter can be easily producedin the injection molding manufacturing process of the light transmissionrods.

In one preferred embodiment, the other ends of the light transmissionrods are bound together so as to form a member for coupling in lightinto said light transmission rods. Such a member may have asubstantially cylindrical shape, a rectangular shape, or any othershape. The light transmission rods may also be bound together into morethan one member. The end surfaces of the bound-together lighttransmission rods can be placed in front of a lamp or other lightsource, a reflector behind the lamp providing a light radiationcomprising substantially parallel light beams, so that there arerelatively small angles between the direction of the light radiation inthe light transmission rods and the longitudinal direction of theserods.

In one preferred embodiment, said plate-like light-guiding member isprovided with means for emitting light through at least part of itsfront surface, i.e. its large surface substantially perpendicular tosaid lateral surface. Such an emission of light may be obtained byroughening of said front surface or the rear surface of thelight-guiding member as described in US-A-2002/0167820.

In another embodiment, said light-guiding member has a substantiallyflat plate-like and triangular shape, wherein a shorter side of thetriangle comprises the lateral surface for coupling in light into saidlight-guiding member, wherein a longer side of the triangle comprises acoupling-out surface which may face a surface of a light-guiding elementfor coupling in light into this light-guiding element, and wherein thethird side of the triangle comprises a number of surfaces that arepositioned at an angle to the direction of said third side, all saidsurfaces being perpendicular to the plane of said plate-like shape,while said light transmission rods are connected to said lateralsurface.

Preferably, the plate-like light-guiding member has a substantiallyright-angled triangular shape, wherein said shorter side and said longerside of the triangle enclose the substantially right angle, and whereinsaid third side is the hypotenuse of the triangle, which side comprisessaid number of surfaces, said surfaces being positioned at an angle ofabout 45° to said coupling out surface.

Preferably, said third side comprises a number of surfaces havingalternating directions, at said angle to the direction of said thirdside and substantially perpendicular to said shorter side.

In this embodiment, the light-guiding member functions as anintermediate optical waveguide, in which the shorter side of thetriangle can be made as short as is required to make use of anappropriate number of light transmission rods, and the longer side mayhave a length corresponding to the length of the oblong lateral surfaceof the plate-like light-guiding element. The number of surfaces at acertain angle along said third side of the triangle is preferably morethan six, more preferably more than twelve.

In one preferred embodiment, at least said surfaces having a directionat an angle to the direction of said third side are provided with alight-reflecting material. All surfaces of the light-guiding member,except for the coupling-out surface, may be provided with alight-reflecting coating to increase the reflection of light if thesurface is not smooth enough to reflect all light having an angle ofincidence greater than the angle of total reflection, or if there arelight beams having an angle of incidence smaller than the angle of totalreflection. Such a coating may also protect the relevant surfaces fromundesired optical contact with other materials.

Preferably, the light-guiding member has a thickness between 0.5 mm and15 mm, more preferably between 2 mm and 7 mm. This thickness preferablycorresponds to the thickness of said light-guiding element, if present.

In one preferred embodiment, said light-guiding element has a plate-likeshape and is provided with means for emitting light through the frontside of the plate, said light transmission rods, said light-guidingmember, and said light-guiding element being one piece of the samematerial, while an interstice extending over a major portion of thecoupling-out surface of the light-guiding member is present between saidlight-guiding member and said light-guiding element. The intersticeforms two mutually facing and substantially parallel surfaces with airin-between, so that only light beams having a smaller angle of incidencethan the angle of total reflection can pass the interstice. There may bemore interstices extending in the same plane with relatively small areasbetween the interstices where the light-guiding member and thelight-guiding element are interconnected. The interstices may beproduced during the injection molding operation or may be madeafterwards, for example by a material-removing operation with a laserbeam.

Preferably, surfaces of the light-guiding member and/or thelight-guiding element and/or the light transmission rods are providedwith a coating having a lower refractive index than the material of saidmember, element, or rods, respectively. Such a coating, or cladding,prevents the surface of the light-guiding material from being contactedby material or becoming contaminated, for example by fingerprints, withmaterial having the same or a higher refractive index making opticalcontact with the surface of the light-guiding material, resulting inundesired coupling-out of light.

For example, such a cladding makes it possible to attach a fabricagainst the front surface of the light-guiding element by means of glue,so that the light can shine through the fabric. Furthermore, thelight-guiding element may be fixed by means of glue while being mounted.

The whole combination of the light-guiding member and the light-guidingelement and the light transmission rods can be made by one injectionmolding operation, so that the assembly containing all light-guidingmeans is one piece of the same material. The light can thus be guidedfrom the light source to the location of emission without losses.

The invention also relates to a method of guiding light by means of alight-guiding system comprising a plate-like light-guiding memberprovided with a lateral surface for coupling in light into saidlight-guiding member, wherein light is coupled in through a number oflight transmission rods, wherein the ends of the light transmission rodsare connected to said lateral surface, and wherein said light-guidingmember and said light transmission rods are one piece of the samematerial.

The invention will now be further elucidated by means of a descriptionof some embodiments of a light-guiding system, wherein reference is madeto the drawing comprising Figures which are only schematicrepresentations, in which:

FIG. 1 is a plan view of a plate-like triangular light-guiding member;

FIG. 2 is a side elevation of the light-guiding member viewed from thelower side in FIG. 1;

FIG. 3 is a side elevation of the light-guiding member viewed from theupper side in FIG. 1;

FIG. 4 is a side elevation of the light-guiding member viewed from theright-hand side in FIG. 1;

FIG. 5 is a sectional view taken on the line V-V in FIG. 1;

FIG. 6 is a plan view of a optical waveguide comprising lighttransmission rods;

FIG. 7 is a side elevation of the optical waveguide viewed from thelower side in FIG. 6;

FIG. 8 is a side elevation of the optical waveguide viewed from theleft-hand side in FIG. 6;

FIG. 9 is a sectional view taken on the line IX-IX in FIG. 6;

FIG. 10 is a plan view of a system for guiding and emitting light;

FIG. 11 is a side elevation of the system viewed from the lower side inFIG. 10;

FIG. 12 is a side elevation of the system viewed from the right-handside in FIG. 10;

FIG. 13 is a side elevation of the system viewed from the upper side inFIG. 10;

FIG. 14 is a sectional view taken on the line XIV-XIV in FIG. 10; and

FIG. 15 is a sectional view taken on the line XV-XV in FIG. 10.

FIG. 1 shows a plate-like and substantially triangular light-guidingmember 1. In this example of an embodiment, the material of thelight-guiding member 1 is polycarbonate, which is a transparentthermoplastic material that can be shaped by means of an injectionmolding operation. The outer surfaces of the product that is produced bythe injection molding operation are smooth, so that light that iscoupled in will be reflected by said surfaces, provided that the angleof incidence with respect to the relevant surface is greater than theangle of total reflection (i.e. the critical angle of total reflection).The angle of total reflection depends on the value of the refractiveindex of the material of the light-guiding member and the value of therefractive index of the medium bordering the relevant surface of thelight-guiding member.

The refractive index of polycarbonate is about 1.6 and the refractiveindex of air is about 1, so the angle of total refraction is about 39°.That means that all light beams having an angle of incidence above 39°with respect to the relevant surface of the light-guiding member 1 willbe totally reflected back into the material of the light-guiding member1. Only a light beam having an angle of incidence smaller than 39° willbe coupled out.

In this embodiment, the light-guiding member 1 has, in plan view, asubstantially right-angled triangular shape, a shorter side 2 and alonger side 3 of the triangle enclosing the substantially right angle 4.In the embodiment shown, the thickness of the plate-like light-guidingmember 1 is about 6 mm.

The shorter side 2 is provided with light-coupling means 5 for couplingin light into the light-guiding member 1. The light-coupling means 5comprise a number of light transmission rods 6 that are positionedparallel to each other in a plane parallel to the plane of theplate-like shape of the light-guiding member 1, at least near thismember 1. The light transmission rods 6 and the light-guiding member 1are produced in one injection molding operation, and therefore they areone integral piece of the same material. FIG. 1 only shows eleven lighttransmission rods 6, but in practice there may be many more lighttransmission rods connected to the light-guiding member 1. The lighttransmission rods 6 may also be located in two of more differentparallel planes.

The longer side 3 comprises a coupling-out surface 7 positionedperpendicularly to the plane of the plate-like light-guiding member 1.FIG. 2 shows the coupling-out surface 7 in front view. Light will becoupled out from the light-guiding member 1 if the light beams have anangle of incidence with respect to the coupling-out surface 7 of lessthan 39°, this being the angle of total reflection in the describedembodiment.

The third side of the triangular shape of the light-guiding member 1,the hypotenuse 8, comprises a number of surfaces 9,10 having alternatingdirections. All surfaces 9 are positioned parallel to the coupling-outsurface 7 and all surfaces 10 are positioned at an angle of 45° to thecoupling-out surface 7. The surfaces 9,10 are positioned perpendicularlyto the plane of said plate-like shape. FIGS. 3 and 4 show the row ofsurfaces 9 and 10 with alternating directions.

FIG. 5 is a sectional view taken on the line V-V of FIG. 1 and shows thelight transmission rods 6 in sectional view. A light transmission rod isalso called a light transmission tube. However, it is not a “tube” (i.e.a hollow body), but for light it is in fact a tube because the light ispropagated in the material of the tube and is reflected against theouter surface of it, so it stays in the tube or rod 6.

The light transmission rod 6 may have a round transverse section, sothat its shape is cylindrical. However, other shapes of the transversesection are possible, for example a hexagonal or a square shape, inorder to facilitate the creation of a bundle without space between thelight transmission rods 6.

The transverse section of the light transmission rods 6 may also varyalong its length, i.e. in one preferred embodiment at least a portion ofa light transmission rod 6 has an increasing diameter in a directiontowards the light-guiding member 1. The light beams will thus becomemore and more parallel when passing through the light transmission rod.Such an increase of the diameter is preferably applied near thelight-guiding member 1 to which the rods 6 are connected, the diameterof the light transmission rods 6 near said member 1 being preferablymore than 1.5 times, more preferably more than twice the diameterfurther away from said light-guiding member. Such an increasing diametercan be easily produced by an injection molding operation of the lighttransmission rods 6.

By means of the light-guiding member 1, light can be coupled in througha relatively small (short) area at the shorter side 2 and can be coupledout through a relatively large (long) area, i.e. the coupling outsurface 7, at the longer side 3. Depending on the manner of coupling inof the light into the light transmission rods 6, the direction of theradiation can be given a very small angle to said longitudinaldirection. Therefore, the radiation of the coupled-in light entering thelight-guiding member 1 through the light transmission rods 6 has a smallangle to the longitudinal direction of the light transmission rods 6 andis therefore directed substantially parallel to the coupling-out surface7.

So, the light enters the light-guiding member 1 mainly with a directionparallel to the coupling-out surface 7. Therefore, almost all coupled inlight will hit one of the surfaces 10 at an angle of incidence of about45°. Since this angle is much greater than the angle of total reflection(being about 39°), most of the light will be reflected in a directionsubstantially perpendicular to the coupling-out surface 7, or with arelatively small deviation from that direction. All light having anangle of incidence smaller than 39° will be coupled-out through thecoupling out surface 7, apart from some small losses of light caused bythe passage through the surface 7.

The light-guiding member 1 functions as an intermediate opticalwaveguide, in which the shorter side 2 of the triangle may be made asshort as is required to make use of appropriate light-coupling means 5and the longer side 3 may have a length corresponding to the length ofthe oblong lateral surface of a plate-like light-guiding element. Thenumber of surfaces 9,10 along the hypotenuse 8 of the triangle can be aslarge as is required to achieve an appropriate reflection anddistribution of the light.

If the angle of total reflection is greater than in this embodimentbecause of the use of other materials or another surrounding medium, orif reflection is disturbed by a less smooth surface, the surfaces 10and/or also other surfaces of the light-guiding member, may be providedwith a light-reflecting material. Such a material, or coating, may alsoprotect the relevant surfaces from undesired optical contact with othermaterials.

Instead of a reflecting coating, a reflecting mirror may be mounted atsome distance to the relevant surface, for example surface 10. There arealso high-reflection tapes available that can be attached to the surfacein order to provide a full reflection of the light back into thematerial of the light-guiding member 1.

Furthermore, the two parallel surfaces of the light-guiding member (thefront surface and the rear surface) may be provided with a coating ofmaterial having a lower refractive index than the material of thelight-guiding member 1 itself. Such a coating, or cladding, prevents thesurface of the light-guiding material from being contacted by materialor becoming contaminated, for example by fingerprints, with materialhaving the same or a higher refractive index making optical contact withthe surface of the light-guiding material, whereby light can be coupledout unintentionally.

FIGS. 6, 7 and 8 show a number of light transmission rods 6 and aportion of the plate-like light-guiding member 1 to which the lighttransmission rods 6 are connected. Near the light-guiding member 1, thelight transmission rods 6 are parallel and positioned in a flat plane,as is shown in FIG. 9, which is a sectional view taken on the line IX-IXin FIG. 6. Further away from the light-guiding member 1, the lighttransmission rods 6 are positioned closer to each other, and at the endall light transmission rods 6 have become a bundle 14 of parallel rods 6surrounded by a cylindrical holder 15.

In order to transport light to the light-guiding member 1 through thelight transmission rods 6, light has to be coupled in into the lighttransmission rods 6 at the other ends of these rods 6, i.e. the endsthat are not connected to the light-guiding member 1. These ends arepresent in the cylindrical holder 15. To couple in light, the holder 15may be placed in front of a lamp or other light source, which is notshown in the drawing. A reflector behind the lamp or a lens in front ofthe lamp can provide light with substantially parallel radiation, whichcan be directed to the cylindrical holder 15, so that the light in eachlight transmission rod 6 has substantially a direction corresponding tothe longitudinal direction of the respective light transmission rod 6.The light will thus enter the light-guiding member 1 mainly in onedirection. If the light-guiding member 1 is a member as shown in FIGS.1-5, said direction of the light radiation is advantageously asdescribed above. If the light-guiding member 1 is a plate-like waveguidefor other purposes, however, for example for emitting light through itsfront side as will be described below, it is also advantageous to havethe light radiation mainly parallel and perpendicular to a lateralsurface of the plate like light-guiding member. The light will then beeffectively distributed in the light-guiding member and will easilyreach locations far away from said lateral surface.

The light transmission rods 6 may have a round transverse section, as isshown in the Figures. However, it may be advantageous to provide thelight transmission rods 6 with someother transverse sectional shape, forexample a hexagonal shape or a square shape. Then the rods 6 can beeasily bound together into a bundle without any space between them. Inthe case of round rods 6, ends of the rods may be heated while beingpressed together in order to eliminate spaces between the rods in thecylindrical holder 15. The rods 6 may even be fused (melted) together inthe holder 15. However, any space between the light transmission rods 6in the holder 15 does not disturb the coupling-in of light into thelight transmission rods 6, but there may be more losses of light in thatcase.

In the embodiment described, the holder 15 has a cylindrical shape.However, the holder may also have another shape, for example arectangular shape should such a shape correspond better to the shape ofthe light source. The light transmission rods 6 may also be divided overmore bundles 14, i.e. more holders 15, in which case the ends of thebundles are located in front of different light sources.

In one preferred embodiment not shown in the Figures, the diameter ofthe rods varies over its length, such that the diameter increases in adirection away from the light-guiding member 1. As was noted above, sucha shape improves the transmission of light in that the transmitted lightbeams are directed more and more parallel to each other during theirtransmission.

The light transmission rods 6 may have a diameter between 0.2 mm and 5mm, preferably between 1 mm and 3 mm, and the distance between the rods6, near the light-guiding member 1, may be between 0.5 mm and 2 mm. Thenumber of light transmission rods 6 may be high, depending on therequirements. The length of a light transmission rod 6 may also dependon the requirements. In general, the lengths of the light transmissionrods 6 are different, to enable each of them to bridge the distancebetween the lateral surface of the light-guiding member 1 and thecylindrical holder 15 in an appropriate way. This distance may be shortif the cylindrical holder 15 with the light source is located near thelight transmission member 1, but it is also possible to place the lightsource and the cylindrical holder 15 far away from the light-guidingmember 1, with the light transmission rods 6 arranged in a bundlerunning from the cylindrical holder 15 to a location near thelight-guiding member 1, where the light transmission rods 6 diverge totheir individual locations at the lateral surface of light-guidingmember 1.

The light transmission rods 6 as well as the light-guiding member 1 towhich the rods 6 are connected are manufactured in an injection moldingoperation. The two parts 1,6 are made together therein, so that they areone piece of material, being polycarbonate in this example of anembodiment, which material allows sufficient flexibility for the lighttransmission rods 6. The light can thus be guided without anyinterruption from the light source at a distance from the light-guidingmember 1 to said plate-like light-guiding member 1, where its entranceis distributed over the entire lateral surface of the light-guidingmember 1, the radiation of the light being directed substantiallyperpendicularly to said lateral surface.

Said other ends of the light transmission rods 6 are formed into abundle 14 and surrounded by the holder 15 after the light transmissionrods 6, together with the light-guiding member 1, have been produced inan injection molding operation. The holder 15 may be a metal or plasticcylinder into which the bundle 14 of light transmission rods 6 isintroduced, it may alternatively comprise two ‘half pipes’ which arejoined together around the bundle 14. As an alternative, the holder 15may consist of tape wound around the bundle 14 of light transmissionrods 6.

FIG. 10 shows an embodiment of a light-guiding system comprising arectangular plate-like light-emitting element 20 and a substantiallytriangular plate-like light-guiding member 21, similar to thelight-guiding member 1 described above, for which reference is made toFIGS. 1-5.

According to FIGS. 11 -13 (side elevations) and FIGS. 14-15 (sectionalviews), the plate-like light-emitting element 20 and the light-guidingmember 21 are flat, but they may also be curved, resulting in a two-orthree-dimensional curved shape. Such a shape may, for example,correspond to the shape of a vehicle roof or a part thereof to which thelight-guiding system is to be mounted. If there are only relatively weakcurves in the plate-like shape, the light will not be coupled outbecause of the curves.

Light is coupled out through front surface 22 of light-emitting element20. To achieve such light emission, radiation of light inside theelement 20 is given a direction corresponding to an angle of incidencetowards the front surface of less than the angle of total reflection. Inorder to obtain such a direction of light radiation, the rear surface 23or the front surface 22 may have, at least locally, a certain structureobtained by roughening, embossing or boring of the surface of thematerial. Another possibility is the introduction of scattering centers,such as refractive pigments, in the material of the light-emittingelement 20. Anyway, such means for coupling out light are known per se.The rear surface 23 of the light-emitting element 20 may be coated withlight-reflecting material to prevent light radiation through said rearsurface 23. It is also possible to mount a mirror at some distance fromthe rear surface 23, so that light is reflected back into thelight-emitting element 20.

In the embodiment shown in FIG. 10, the light-emitting element 20 andthe light-guiding member 21 are connected to each other in fourlocations 24. Between these locations 24 there are three interstices 25which cover a major portion of the area between the light-emittingelement 20 and the light-guiding member 21. Although an interstice 25may extend over a portion of the distance between the front surface 22and the back surface 23, so that one of the surfaces 22,23 isuninterrupted, the interstices 25 in the embodiment shown extend overthe entire thickness of the light-emitting element 20 and light-guidingmember 21, as is clearly shown in FIG. 15. The width of the intersticesin this embodiment is about 1 mm. Preferably, the width of theinterstices is between 0.05 and 0,15 times the thickness of thelight-guiding member 1.

The light-emitting element 20 and the light-guiding member 21 and thelight transmission rods 6 are one piece of the same material, in thisembodiment polycarbonate, manufactured in one injection moldingoperation. The interstices 25 are also formed during that injectionmolding process. However, the interstices 25 may alternatively be madeafterwards, for example by a material-removing operation with a laserbeam.

As described above with reference to the substantially triangularlight-guiding member 1, the light enters the light-guiding member 21through the light transmission rods 6, the direction of the lightradiation being mainly parallel to the longitudinal direction of therods 6. Then the light is reflected by the surfaces 10 and sent in thedirection of the light-emitting element 20, during which most of thelight radiation has a direction substantially perpendicular to theinterstices 25. This light will cross the interstices 25 with smalllosses because it passes both surfaces of the interstice 25. However,light radiation having a direction with a large angle to a lineperpendicular to the interstice 25 will not cross the interstice 25, butwill be reflected back into the material of the light-guiding member 21.This light radiation can only cross the interstice 25 after beingreflected in the light-guiding member 21 once or several times, untilits direction allows the passage through the interstice 25.

Owing to the interstices 25, therefore, the light coupled into thelight-emitting element 21 has a direction whereby it can easily reachlocations at a relatively large distance to the surface where the lightenters the light-emitting element 20. This improves the distribution ofthe light emission over the front surface 22 of the light-emittingelement 20.

Furthermore, the presence of the interstices 25 improves the guidance oflight from the light transmission rods 6 to the surface 10 on theright-hand side of FIG. 10, i.e. far away from the rods 6. If a lightbeam from a lower (in FIG. 10) light transmission rod 6 divergesdownwards, it will be reflected by the surface of the interstice 25 andbe directed to the surface 10 on the right-hand side of FIG. 10.

The light-guiding member 21 and/or the light-emitting element 20 and/orthe light transmission rods 6 may be provided with a coating having alower refractive index than the material of said member 21, element 20,or rods 6, respectively. Such a coating, or cladding, prevents thesurface of the light-guiding material from being contacted by materialor becoming contaminated, for example by fingerprints, with materialhaving the same or a higher refractive index making optical contact withthe surface of the light-guiding material, resulting in undesiredcoupling-out of light. For example, such a cladding makes it possible toattach a fabric against the front surface of the light-emitting elementby means of glue, such that the light can shine through the fabric. Thecladding also allows the fixation of the light-guiding system by meansof glue.

The embodiments described above are merely examples of the light-guidingsystem; a great many other embodiments are possible.

1. A light-guiding system comprising a plate-like light-guiding memberprovided with a lateral surface for coupling in light into saidlight-guiding member, characterized in that the ends of a number oflight transmission rods are connected to said lateral surface, saidlight-guiding member and said light transmission rods being one integralpiece of the same material.
 2. A light-guiding system as claimed inclaim 1, characterized in that, near said lateral surface, the lighttransmission rods are positioned parallel to each other in a planeperpendicular to said lateral surface.
 3. A light-guiding system asclaimed in claim 1, characterized in that the distance between the lighttransmission rods, near said lateral surface, is less than 5 mm,preferably between 1 mm and 2 mm.
 4. A light-guiding system as claimedin claim 1, characterized in that the light transmission rods have adiameter between 0.2 mm and 5 mm, preferably between 1 mm and 3 mm.
 5. Alight-guiding system as claimed in claim 1, characterized in that saidlight-guiding member and the light transmission rods are produced by aninjection molding process.
 6. A light-guiding system as claimed in claim1, characterized in that at least a portion of a light transmission rodhas a hexagonal or a square transverse section.
 7. A light-guidingsystem as claimed in claim 1, characterized in that at least a portionof a light transmission rod has a diameter that increases in a directiontowards the light-guiding member.
 8. A light-guiding system as claimedin claim 1, characterized in that the other ends of the lighttransmission rods are bound together so as to form a member for couplingin light into said light transmission rods.
 9. A light-guiding system asclaimed in claim 1, characterized in that said light-guiding member isprovided with means for emitting light through at least part of itsfront surface.
 10. A light-guiding system as claimed in claim 1,characterized in that said light-guiding member has a substantially flatplate-like and triangular shape, wherein a shorter side of the trianglecomprises the lateral surface for coupling in light into saidlight-guiding member, wherein a longer side of the triangle comprises acoupling-out surface which may face a surface of a light-guiding elementfor coupling in light into said light-guiding element, and wherein thethird side of the triangle comprises a number of surfaces that arepositioned at an angle to the direction of said third side, all saidsurfaces being perpendicular to the plane of said plate-like shape, saidlight transmission rods being connected to said lateral surface.
 11. Alight-guiding system as claimed in claim 10, characterized in that saidlight-guiding element has a plate-like shape and is provided with meansfor emitting light through the front side of the plate, and in that saidlight transmission rods, said light-guiding member, and saidlight-guiding element are one integral piece of the same material, andone or more interstices extending over a major portion of thecoupling-out surface between said light-guiding member and saidlight-guiding element.
 12. A light-guiding system as claimed in claim 1,characterized in that surfaces of the light-guiding member and/or thelight-guiding element and/or the light transmission rods are providedwith a coating having a lower refractive index than the material of saidmember, element, or rods, respectively.
 13. A method of guiding light bymeans of a light-guiding system comprising a plate-like light-guidingmember provided with a lateral surface for coupling in light into saidlight-guiding member, characterized in that light is coupled in througha number of light transmission rods, wherein the ends of the lighttransmission rods are connected to said lateral surface, and whereinsaid light-guiding member and said light transmission rods are oneintegral piece of the same material.